Parametric amplification in a glass optical fiber is a third order nonlinear process dependent upon χ(3) third order nonlinearity properties of the glass. Parametric amplification operates by the process of four wave mixing involving the interaction of four optical waves. In parametric amplification processes, one and/or two laser pump and/or signal pump waves pumped at frequencies ω1 and/or ω2 amplify a signal wave at a frequency ω3 and generate an idler wave at a frequency ω4. When a given parametric amplification process has a single (i.e., one) laser pump and/or signal pump wave, then ω1=ω2. The frequencies of the signal wave and the idler wave are related to the frequencies of the laser pump wave and/or signal pump wave by the relation represented as: ω3+ω4=ω1+ω2.
Parametric amplification has been demonstrated in media of varying compositions, such as silica fiber at near IR wavelengths and visible light wavelengths; however, parametric amplification has not been achieved in the mid IR wavelengths. Therefore, the need exists for fiber optic media of varying compositions that will facilitate parametric amplification in the mid IR wavelengths. Furthermore, in order to utilize parametric conversion to generate light in the mid IR wavelengths, a medium which is transparent in the mid IR wavelengths is necessary. Chalcogenide glass fiber is such a medium and has a wavelength transmission range of from about 0.8 micrometers to about 14 micrometers (μm), depending upon the composition of the chalcogenide glass fiber.
Efficient parametric amplification requires light transmitting media having qualities providing high fiber nonlinearity effects. Therefore, the need exists for fiber optic media having qualities providing high fiber nonlinearity effects. Chalcogenide glasses have demonstrated third order (X(3)) nonlinearities, approximately 900 times higher than silica. Thus, fibers made from chalcogenide glasses demonstrate efficient nonlinear conversion characteristics.
Photonic crystal fiber is optical fiber whose guiding solid core region is surrounded by air holes. The solid glass core forms the cladding of the chalcogenide photonic crystal fiber. The air holes create a reduced index cladding which contains light in the solid core region. The advantage of photonic crystal fiber over conventional core/clad fiber is that the dispersion of the fiber can be more easily tailored by manipulating cladding microstructured hole size and periodicity, as well as, core size. In photonic crystal fiber, very small core sizes are obtainable, resulting in increased nonlinearities in the fiber.
Efficient parametric amplification also requires careful control of the dispersion of the fiber to achieve phase matching of the laser pump waves, signal waves and idler waves. In solid core chalcogenide fiber and chalcogenide photonic crystal fiber, efficient parametric amplification can be controlled by (1) the design characteristics of the core of the fiber media and/or (2) the design characteristics of the cladding of the fiber media and/or (3) the selection and design of the material composing the core and/or (4) the selection and design of the material composing the cladding. Therefore, the need exists for a method of controlling the dispersion of the fiber by controlling the selection and design of the core and cladding of the fiber.
There are only a few commercial sources of high brightness infrared (IR) radiation. IR Blackbody sources are highly broadband, but are very low power emitters. Optical Parametric Oscillator (OPO) sources, IR diode lasers, gas lasers, and IR solid sate lasers are complex, bulky, and expensive. There are no known tunable sources in the mid IR wavelength ranges. Tunable sources are desirable for current light detection and ranging (LIDAR), infrared countermeasures (IRCM) and ranged chemical and/or biological sensor systems, and IR illuminators as well as, IR fiber and free space communication systems. Therefore, the need exists for parametric amplifiers in the IR wavelength range having high power tunable IR generators in a simple and efficient configuration.